The present invention relates generally to loose fill packing materials or "dunnage," as they are sometimes referred to, such as packing "chips" or "peanuts," and to molds and methods for forming them.
As suggested by their name "loose fill" packing materials are used to surround an article being shipped within a container or package to prevent movement of the article within the container and to prevent contact between the article's surface and the interior surfaces of the container. Simply stated, loose fill packing material is intended to cushion the article or articles being shipped from the forces which may be exerted on the exterior of the container during shipment. The present invention provides a method for preparing an improved loose fill packing material.
The suitability of any loose fill material is judged by certain functional characteristics. Among other things, loose fill packing material should be strong and have structural integrity, while providing the necessary cushioning properties. It should be light weight and should not nest or settle. The total volume of the loose fill packing should not diminish during shipment and/or storage of the article and container, notwithstanding vibration, shaking or other movements imparted to the container. The loose fill packaging material should be relatively free-flowing and static-free, qualities that enhance the ability to dispense it into the container and around the article during packing. Obviously, any loose fill packing materials should be as inexpensive as possible.
In recent years, expanded plastic foam, primarily polystyrene, has been frequently utilized as loose fill packing material. Although formed into a variety of shapes including, for example, hollow cups, saucers and S-shapes, they are frequently referred to as "peanuts." These plastic peanuts exhibit certain desirable cushioning properties. On the other hand, they also have certain highly undesirable qualities. Principal among these is the fact that plastic peanuts are not easily recyclable or biodegradable and, therefore, are environmentally unfriendly. Whether they come to rest in a neighbor's lawn or in a public landfill, they do not deteriorate. They litter the landscape and take up unnecessary landfill space. Unless reused as packing material, plastic peanuts from an unpacked container are virtually useless. Frequently, plastic peanuts exhibit static build-up, making them annoying to work with. Children and pets may ingest plastic peanuts, causing choking, suffocation, illness or death.
The negative qualities of plastic peanuts have provided incentives to prepare dunnage from natural, environmentally friendly materials. For example, efforts have been expended to make loose fill packing from organic material, such as wood fibers bound together with starch or other adhesives and formed into the appropriate shape. This type of dunnage is relatively expensive to make; the manufacturers have charged a premium in excess of the price of plastic peanuts. These materials have a number of other defects, including the fact that products containing significant amounts of starch may attract rodents or pests.
Attempts have also been made to manufacture loose fill packing from recycled paper, particularly recycled newspaper. Examples are described in U.S. Pat. No. 4,997,091 to McCreu, 5,151,312 to Boeri, 5,230,943 to Pregont, 5,372,877 to Kannankeril, and 5,382,325 to Warda et al. The latter patent is assigned to the same assignee as the present invention. These materials are manufactured by molding the individual pieces of loose fill packing material from a pulp of recycled paper and water.
Generally, the molding of paper "pulp" into products, such as egg cartons, has utilized processes like the rotary vacuum forming machine illustrated schematically in FIG. 1.
As illustrated in FIG. 1, cylinder 150 contains molds, such as 160, extending outward from the periphery of the cylinder. Typically, each mold is made from a "screen," i.e., metal mesh, having the shape of the interior of the finished molded article. The cylinder 150 rotates in a clockwise direction as the molds proceed continuously through various stages in the process. These stages are illustrated at positions A through H in FIG. 1. FIG. 1 is not drawn to scale and is for the purposes of comparison only.
At position A, the mold 160 is dipped into the aqueous cellulose pulp 175 in pulp tray 170. Simultaneously, a vacuum is applied toward the inside of the mold in the directions shown by arrows 172 (using equipment not illustrated) to pull the pulp in the pulp tray against the mold screen. As water is pulled through the screen, the cellulose paper pulp is caught on the screen to form the molded article. Water, however, does pass through the screen. The vacuum continues to be applied until a molded article of the appropriate thickness has been formed in the interstices of the mold 160.
As the cylinder revolves further, the screen containing the crude article of molded pulp is rotated out of the pulp tray 170. Additional water is removed by inverting the mold at position E. At position G, it is brought adjacent to a press and transfer drum 180. The drum contains molds 181 which mate with mold 160 and conform with the exterior shape of the molded article. By movement of the drum 180 in a counter-clockwise direction, the mating mold is brought into position (not shown) where it contacts the partially molded pulp thereby pressing the pulp against the screen 160 to form the pulp into the shape of the final article and forcing out excess water. Removal of the excess water is important to minimize the energy requirements of drying, which may constitute one of the most significant costs in producing the molded product. Upon completion of the molding, the press and transfer drum is rotated in a counter-clockwise direction to separate the two molds. As this rotation is commenced, a positive blast of air (sometimes called "blow-off") is directed through the screen 160 (via equipment now shown) in the direction of arrows 182 to separate the pulp from the mold 160. The vacuum then holds the resulting molded article loosely in the mating mold 181 until the press and transfer drum 180 reaches a position where the molded article is released down to conveyor 185. The molded article and others like it are then passed via the conveyor through a dryer 186 for a sufficient period of time to remove the remaining water and produce the finished product.
The cylinder 150 continues to rotate the mold 160 through position H. In position H the mold is brought adjacent to spray-off station 190, where it is contacted with water to clean it in preparation for the next molding step at position A.
Although this process is used commercially, it is far from perfect in a number of respects. Among other things, it is impossible to continuously and reliably prepare multiple, small thin-walled articles, such as loose fill packing material, with this equipment. This is unfortunate, since cellulose packing material is preferably made with the thinnest possible walls. This generally improves its qualities as a packing material. More importantly, thin-walled, cellulose packing material biodegrades completely in a shorter period of time.
The inability of prior art processes to produce thin-walled cellulose packing material is caused, in part, by the fact that the intermediate pulp article prepared on the screen usually contains excess moisture. Excess moisture reduces the structural stability of the formed pulp article, making it impossible to produce a thin-walled article with enough structural integrity to be successfully removed from the screen via conventional blow-off techniques. Moreover, the pressing of molds 160 and 181 (at position G illustrated in FIG. 1) forces the molded article into the interstices of the screen 160. When that article is thin-walled, the subsequent blow-off step is difficult to successfully perform without breaking, tearing or cracking the article. While it might be possible to eliminate the pressing step at station G, separation of a thin-walled molded article from the screen is still difficult. This is further complicated by the height at which such a separation would occur, resulting in destruction or mutilation of the wet pulp article when it lands on the conveyor. Where multiple articles are being molded simultaneously, removal is further complicated by the fact that positive blow-off pressure is lost as soon as one of the articles is removed from the screen.
It is particularly difficult to continuously and reliably prepare a thin-walled article from recycled newsprint and other recycled papers. Generally, newsprint has relatively short fibers which significantly reduces the strength of the wet molded articles during the intermediate processing steps.
It has now been discovered that thin-walled packing chips of paper pulp can be prepared reliably and efficiently utilizing the process of the present invention. As used herein, the term "chip" is intended to mean an individual unit of loose fill packing material or dunnage. Unless otherwise indicated, the use of this term is not intended to imply that the chip has any particular shape. Thin-walled packing chips have improved biodegradability. Surprisingly, the thin-walled packing chips of the present invention also have improved characteristics important to their performance as loose fill packing material.